Flusing water pipes after soldering

Does anyone know how long or how much you should flush copper water pipes
after soldering? It seems to me that the water retained a flux odor for
quite a while, and was wondering if there was any rule of thumb about how
long to flush before the water is potable.

That depends on who's drinking it. For me, 2000 gallons. For you,
a pint......
Seriously, all I've done is let it run for maybe 10 gallons or so. I
doubt there is anything more harmful in the flux than other things we
are all routinely exposed to. Even if you let it run longer, given
the compostion of flux, unless it were very hot water, I doubt any
more is going to come off. With a few gallons you would likely
dislodge any little chunks of debris, but if it's simply flux inside a
cold water pipe, it might take hundreds of thousands of gallons to
erode every last bit of flux.

I didn't think so. The hot water was discolored for a while, way too much
for the flux to be the culprit. I can't identify the odor, either. I have a
small pot of flux, and I used less then a tablespoon for the entire job.
I'm suspecting some comtamination in the copper pipes themselves. If that
isn't it, could turning the water on and off several times break loose gunk
in the water heater? The cold water did not run discolored at all, it just
quickly flushed out a few pockets of stuff and has been clear since. Weird.

It's quite normal to have discolored hot water after draining and
refilling the plumbing. To know that it's running clear again, fill
the bathtub. Slight discoloration will show up a lot better that way.

That is the crap from the bottom of your hot water heater...
That is a bad sign... How old is the water heater ???
Is it electric or gas ??? When the bottom of a hot
water heater tank fills up with sediment bad things
happen... I have seen a water heater that had so much
sediment in it that the lower electric element was completely
covered by it...
When was the last time you checked the sacrificial
anode rod in the tank ???
If it is just sediment (dirt) and not rust and hard water
scale) you might have issues with your water supply
pipe from the street or your nearby water mains might
be ready to fail since sand and dirt is getting into your
water tank... You should consider installing a water
filter on the supply line to the water tank if you discover
excessive sediment in your tank...
~~ Evan

The heater is maybe ten years old. Electric. I pulled the plug off of the
bottom and flushed it out about three years ago. We have very soft water
here. Hmm... a month or so ago they went around flushing the water pipes
through the fire hydrants, and our water was murky for a while. It could
be that gunk settled in the bottom of the heater tank at that time. Maybe
time to flush the tank again...

If that ever happen again, shut off your water main and the valve to the heater
while they flush, then open a hose faucet pipe-wise-near the pipe bringing water
into the house and turn on the water again until the hose faucet runs clear, so
you don't bring the muck into your house piping.
When I replaced the water main into my rental house, I added an outdoor
"freeze-proof hydrant" at the property line near the meter. That'll work great
for flushing in the future - nothing will get into the house piping.
For now, a good flush of your water heater might help.

Good luck with that -- your electric water heater is at or nearing the
end of
its useful lifespan... When it does die, you should remove the lower
heating
element and look inside the tank after you drain it to see how much
crap
every drop of hot water you use soaks in while it is in the tank...
You will definitely want to install a water filter on the line feeding
into your
hot water tank after you see the insides of one... When was the last
time
you checked the sacrificial anode rod inside the tank???
~~ Evan

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